1. Field of the Invention
The present invention relates to a retention mold for bonding a tire tube to make an annular tire tube. Both ends of a tube blank which has thickened parts for reinforcement are horizontally retained, protruding from an outer wall surface of freely opening and closing retention molds. The ends of the tube blank are then bonded to each other.
2. Description of Related Art
If a radial load acts on a vehicle wheel which has tube tires, the shape of the tire and the tube change as a result of the load. In particular, when a tire runs aground on hard obstacles such as rocks when travelling off-road or when a tire hits the ground after a vehicle lands from a jump, the tube is subjected to a large pinching pressure between the tire, whose shape has been largely deformed, and a metal rim. Therefore, a rim strike phenomenon arises where respective inner wall surfaces of the tube are brought into contact with each other. If the respective inner wall surfaces of the tube are brought into contact with each other as a result of the rim strike phenomenon, the durability of the contacting parts is sometimes reduced.
A way of preventing the above described lowering of the durability has been disclosed in Japanese Patent Laid-open No. Hei. 9-164806. The tube of this reference includes thickened portions for reinforcement which project from the wall surfaces of a tube that is likely to suffer from damage due to the rim strike phenomenon.
An annular tire tube is manufactured by horizontally retaining both ends of a tube blank with freely opening and closing retention molds and bonding together both ends of the tube blank. However, if the tube blank is retained by retention molds which have flat holding surfaces, the above described thickened portion becomes a hindrance and it is not possible to reliably hold the tube blank. Therefore, warping occurs in the tube blank and precise bonding of the ends of the tube blank becomes difficult. This problem is particularly striking when there are-thickened portions projecting from outer wall surfaces of the tube blank directly contacting the retaining surfaces of the retention molds.
The present invention has been conceived in view of the above described problems. The object of the present invention is to provide a retaining mold for tire tube bonding that enables precise bonding of a tube blank having thickened portions projecting from outer wall surfaces of the retaining mold.
In order to achieve the above described object, the present invention provides a retention mold for bonding a tire tube, for forming an annular tire tube by horizontally retaining both ends of a tube blank, which has thickened parts for reinforcement, protruding from an outer wall surface of freely opening and closing retention molds and bonding both ends together, wherein indents for engaging with the thickened parts are formed in retention surfaces of the retention molds coming into contact with an outer wall surface of the tube blank.
With the above described construction, when both ends of the tube blank are horizontally retained in the freely opening and closing retention molds and bonded together, it is possible to hold the material without warping being caused and to achieve precise bonding by forming indents on the holding surfaces of the retention molds for engaging with the thickened parts projecting from the outer surfaces of the tube blank.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.